The 1991 Infiniti M30 is essentially a luxury-trimmed Nissan Leopard with the VG30E V6. It's a rare bird with good bones but suffers from age-related fuel system issues, transmission cooling failures, and catastrophic engine problems when maintenance history is poor.
VG30E Lower Engine Failure (Piston Ring / Bearing Wear)
Occasional · high severityTypical onset: 120,000-180,000 mi
Symptoms: heavy oil consumption (quart per 500-1000 mi), blue smoke on startup or acceleration, rod knock or main bearing rumble, low oil pressure at idle when hot
Fix: VG30E non-turbo engines with neglected oil changes develop severe piston ring wear and eventually bearing failure. Requires complete engine rebuild (pistons, rings, bearings, machine work) or used/reman replacement. Plan on 18-24 hours labor for in-chassis rebuild, 12-16 for swap if you source a good core.
Estimated cost: $3,500-6,500
Transmission Oil Cooler Line Failure
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: pink or milky transmission fluid, transmission slipping or delayed engagement, coolant in ATF or ATF in coolant, transmission overheating
Fix: The external cooler lines rust through or the internal radiator cooler fails, cross-contaminating ATF and coolant. Requires new cooler lines, radiator replacement if internal cooler failed, full ATF flush (sometimes multiple), and often transmission rebuild if caught late. If you see strawberry milkshake fluid, stop driving immediately. 4-6 hours for lines and radiator, add 12-20 if trans needs rebuild.
Estimated cost: $800-1,200 (lines/radiator only); $2,500-4,000 (with trans rebuild)
Fuel Injector Clogging and Fuel System Varnish
Common · medium severityTypical onset: 90,000+ mi
Symptoms: rough idle and stumbling, hesitation on acceleration, poor fuel economy, hard cold starts, check engine light with lean codes
Fix: Aged fuel in long-stored cars and varnish buildup clog injectors and fuel filter. Recall addressed some early fuel injection issues but age is the real enemy. Professional ultrasonic injector cleaning or replacement set, new fuel filter, intake cleaning. 3-5 hours labor.
Estimated cost: $400-900
Transmission Mount Collapse
Common · low severityTypical onset: 70,000-120,000 mi
Symptoms: clunk when shifting from park to drive or reverse, excessive drivetrain movement felt through chassis, vibration at idle in gear
Fix: Rubber transmission mount deteriorates and allows excessive movement. Replacement is straightforward but requires supporting the transmission. 1.5-2 hours labor.
Estimated cost: $200-350
Head Gasket Seepage (Both Banks)
Occasional · medium severityTypical onset: 100,000-150,000 mi
Symptoms: minor external coolant weeping at head/block junction, slow coolant loss without visible leaks, slight oil in coolant or coolant in oil (if advanced), white exhaust smoke if combustion chamber breach
Fix: VG30E head gaskets can weep externally or fail internally. If caught early as seepage, you can monitor, but once it's mixing fluids or pressurizing the cooling system, both heads must come off. Resurface heads, new gaskets, timing belt and water pump while you're in there. 14-18 hours labor.
Estimated cost: $2,200-3,500
Front Seat Belt Buckle Assembly Failure
Occasional · medium severitySymptoms: buckle won't latch or release properly, buckle button sticks or doesn't engage, recall-related issue on some VINs
Fix: NHTSA recall 91V149000 addressed buckle assemblies that could unlatch unexpectedly. Check if your VIN was covered and if recall was performed. Replacement buckle assembly is the fix. 0.5-1 hour per side.
Estimated cost: $150-300
Buy only with bulletproof service records and recent timing belt; budget $2-3k reserve for deferred maintenance on any example, and walk away from high oil consumption or milkshake ATF.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.